1. Field of the Invention
The present invention relates to an ink ribbon cassette using an endless type ink ribbon.
2. Related Background Art
FIG. 1 shows an ink ribbon cassette using an endless type ribbon. In FIG. 1, an endless type fabric ribbon 2 is enclosed in an enclosing portion 1a in a casing 1. The ribbon pulled out of the enclosing portion 1a is pressed to an inner wall 1b by a tension spring 3 in the portion A. Thereafter, the ribbon is pulled out to the outside.
The ink ribbon pinched by a pressing roller 4 and a gear portion (not shown) of a cassette knob 5 is pulled in the direction of a by the rotation in the direction indicated by an arrow of the cassette knob and again enclosed into the enclosing portion 1a.
However, according to the conventional ink ribbon cassette, when the ink ribbon is slightly pulled out and released, a slack occurs. In addition, according to the conventional cassette, since the surface of the ink ribbon is always rubbed by the tension spring, the ribbon is easily damaged. On the other hand, in the case of the fabric ribbon, when the ribbon is pressed by the tension spring, the ink in the ribbon comes oozing out of the ribbon and the collected ink is carried by the ribbon out to the outside, so that a variation in concentration upon printing is likely to occur.
FIG. 2 shows a general ink ribbon cassette using a fabric ribbon.
A casing 11 consists of upper and lower casings. A ribbon 13 is irregularly piled and enclosed in an enclosing portion 12. The enclosed ribbon 13 passes through a plurality of substantially &lt;-shaped ribs 14 which are formed integrally with the upper and lower casings. The ribbon 13 then passes between a pair of rollers 15 and 16. Thereafter, the ribbon 13 is guided by a pair of arms 17 and 18 so as to be exposed to the outside. The exposed ribbon 13 is moved into engagement with and pinched by a feed gear (not shown) and a pressing gear 20 which are formed integrally with a feed knob 19. When the feed knob 19 rotates in the direction of an arrow, the ribbon is wound in the direction of a and again enclosed into the enclosing portion 12.
The ribs 14 have the function to prevent the ribbon in the enclosing portion 12 from rushing between the pair of rollers 15 and 16 when the ribbon is taken up by the feed knob 19 and enclosed into the enclosing portion 12.
According to the ribbon cassette having such a structure, hitherto, the ribs 14 are formed as shown in FIG. 3. Namely, the ribs 14 are respectively vertically projected from an upper casing 11a and a lower casing 11b and vertical riser portions 14a obstruct the smooth feeding motion of the ink riboon.